I made a sensor board that needs to operate at about -55 degrees Celcius. Unfortunately, its key component often malfunctions when the circuit is cooled for days at the temperature and then powered up. The sensor starts to operate normally after it runs (improperly) for several minutes since the power-up time. Thus I want to warm the board up and then power up the sensor.
There are environmental conditions that make it very difficult to use a simple solution. An external heater cannot be used, because I have no more space than the space for the PCB itself(3cm x 3cm x 5mm). It seems the only feasible approach is to heat the board by adding several SMD components to the PCB circuit, for example, a linear voltage regulator and resistors. The max. power supply is limited to 0.5W, but the sensor IC already consumes up to 0.3W. Thus the sensor and the heater cannot run at the same time. I might have to heat the PCB first and power up the sensor. The allowed time for the heating is up to 30s.
Could you please suggest efficient solutions to the problem? I wonder if there is a better solution than to place a linear regulator with a heat-sink and 2 to 4 0603(1608)-size resistors around the sensor IC. By the way, the board has 4 layers(top/power/GND/bottom) and the copper content is 1oz.